This invention relates generally to crystalline propylene polymer compositions, to methods for their production and to methods for their use in oriented film applications. Specifically, this invention relates to crystalline propylene polymer compositions comprising both propylene homopolymer and propylene copolymer components. Preferably the propylene polymer composition is isotactic. The compositions are prepared using metallocene catalyst systems comprising at least two metallocenes in a polymerization process that involves the sequential or parallel polymerization of propylene homopolymer and copolymer using propylene with a small amount of comonomer, preferably ethylene. The resulting polymer compositions are excellent for use in the production of oriented films. Films prepared with these propylene polymers have a significantly broader processability range and can be evenly stretched at lower temperature compared to films prepared from traditional propylene-based polymers.
Oriented polypropylene films are widely used in tape applications and in packaging applications such as food packaging. The optimization of processing characteristics and film properties of propylene based films has been the subject of intense effort. U.S. Pat. No. 5,118,566, for example, describes a biaxially oriented film made from polypropylene, a natural or synthetic resin, and a nucleating agent. The process for producing this film includes biaxially drawing the film at temperatures below the melting point of the polypropylene.
The present inventors have discovered crystalline propylene polymer compositions made by polymerizing propylene in one stage and then propylene and a minor amount of comonomer in a separate stage using a metallocene catalyst system comprising at least two metallocenes in each of the stages. The resulting polymers have surprisingly high molecular weight and broad molecular weight distribution, and offer processability benefits in oriented film applications. Films made from these unique polymers have a significantly broader processability range and can be evenly stretched at lower temperatures compared to the polypropylene films available today. The resulting films have a favorable balance of properties including high strength, good optical properties and good barrier properties.
Multiple stage polymerization processes are known in the art as is the use of multiple metallocenes, however, multiple stage polymerization processes are usually used to prepare block copolymers which contain rubbery materials as opposed to the crystalline polymers of this invention. U.S. Pat. Nos. 5,280,074; 5,322,902, and 5,346,925, for example, describe two-stage processes for producing propylene block copolymers. The propylene/ethylene copolymer portion of these compositions is a non-crystalline, rubbery material suitable for molding applications rather than films. U.S. Pat. No. 5,350,817 and Canadian Patent Application No. 2,133,181 describe the use of two or more metallocenes for the preparation of isotactic propylene polymers, however, neither reference describes a multiple stage process for the production of crystalline polymer compositions such as those described herein.
In one embodiment, the present invention provides for crystalline propylene polymer composition comprising:
(a) from 10 to 90 weight percent of a crystalline propylene homopolymer composition comprising a first propylene homopolymer and a second propylene homopolymer; and
(b) from 90 to 10 weight percent of a crystalline propylene copolymer composition comprising a first propylene copolymer and a second propylene copolymer, the first propylene copolymer and second propylene copolymer comprising from 0.05 to 15 weight percent (based on the total weight of the crystalline propylene polymer composition) of a comonomer;
wherein the crystalline propylene polymer composition has a molecular weight distribution (Mw/Mn) in the range of from 2.1 to 10; and
wherein the propylene homopolymer composition and the propylene copolymer composition are obtained in separate stages using a single metallocene catalyst system comprising two different metallocene catalyst components.
In another embodiment, the two different metallocenes catalyst components are represented by the formula: 
wherein M is selected from the group consisting of titanium, zirconium, hafnium, vanadium niobium, tantalum, chromium, molybdenum and tungsten;
R1 and R2 are identical or different, are one of a hydrogen atom, a C1-C10 alkyl group, preferably a C1-C3 alkyl group, a C1-C10 alkoxy group, a C6-C10 aryl group, a C6-C10 aryloxy group, a C2-C10 alkenyl group, a C2-C4 alkenyl group, a C7-C40 arylalkyl group, a C7-C40 alkylaryl group, a C8-C40 arylalkenyl group, or a halogen atom;
R3 and R4 are hydrogen atoms;
R5 and R6 are identical or different, and are one of a halogen atom, a C1-C10 alkyl group which may be halogenated, a C6-C10 aryl group which may be halogenated, a C2-C10 alkenyl group, a C7-C40-arylalkyl group, a C7-C40 alkylaryl group, a C8-C40 arylalkenyl group, a xe2x80x94NR215, xe2x80x94SR15, xe2x80x94OR15, xe2x80x94OSiR315 or xe2x80x94PR215 radical, wherein R15 is one of a halogen atom, a C1-C10 alkyl group, or a C6-C10 aryl group;
R7 is 
xe2x80x94B(R11)xe2x80x94, xe2x88x92Al(R11)xe2x80x94, xe2x80x94Gexe2x80x94, xe2x80x94Snxe2x80x94, xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, xe2x80x94SOxe2x80x94, xe2x80x94SO2xe2x80x94, xe2x80x94N(R11)xe2x80x94, xe2x80x94COxe2x80x94, xe2x80x94P(R11)xe2x80x94, or xe2x80x94P(O)(R11)xe2x80x94;
wherein:
R11, R12 and R13 are identical or different and are a hydrogen atom, a halogen atom, a C1-C20 alkyl group, a C1-C20 fluoroalkyl group, a C6-C30 aryl group, a C6-C30 fluoroaryl group, a C1-C20 alkoxy group, a C2-C20 alkenyl group, a C7-C40 arylalkyl group, a C8-C40 arylalkenyl group, a C7-C40 alkylaryl group, or R11 and R12, or R11 and R13, together with the atoms binding them, can form ring systems;
M2 is silicon, germanium or tin;
R8 and R9 are identical or different and have the meanings stated for R11;
m and n are identical or different and are zero, 1 or 2, m plus n being zero, 1 or 2; and
the radicals R10 are identical or different and have the meanings stated for R11, R12 and R13 and two adjacent R10 radicals can be joined together to form a ring system.
In yet another embodiment, the invention provides for a crystalline propylene polymer composition comprising:
(a) from 10 to 90 weight percent of a isotactic crystalline propylene homopolymer composition comprising a first propylene homopolymer and a second propylene homopolymer, the isotactic crystalline propylene homopolymer composition having a molecular weight distribution of less than 3.0; and
(b) from 90 to 10 weight percent of a crystalline propylene copolymer composition comprising a first propylene copolymer and a second propylene copolymer, the first propylene copolymer and second propylene copolymer comprising from 0.05 to 15 weight percent (based on the total weight of the crystalline propylene polymer composition) of a comonomer, the crystalline propylene copolymer composition having a molecular weight distribution of less than 3.0;
wherein the crystalline propylene polymer composition has a molecular weight distribution (Mw/Mn) in the range of from 2.1 to 10; and
wherein the isotactic crystalline propylene homopolymer composition and crystalline propylene copolymer composition are obtained in separate stages using a single metallocene catalyst system comprising two different metallocene catalyst components.
In another embodiment, the invention provides for a process for preparing a crystalline propylene polymer composition comprising the steps of:
(a) polymerizing propylene in a first stage;
(b) copolymerizing propylene and a comonomer in a second stage; and
(c) recovering the crystalline propylene polymer composition comprising from 0.05 to 15 weight percent of a comonomer (based on the total weight of the crystalline propylene polymer composition);
wherein the steps (a) and (b) are conducted in the presence of a single metallocene catalyst system comprising two different metallocene catalyst components.
The invention also provides for a film comprising a crystalline propylene polymer composition comprising:
a) from 10 to 90 weight percent of a crystalline, isotactic propylene homopolymer composition comprising a first propylene homopolymer and a second propylene homopolymer; and
b) from 90 to 10 weight percent of a crystalline propylene copolymer composition comprising a first propylene copolymer and a second propylene copolymer, the first propylene copolymer and second propylene copolymer comprising from 0.05 to 15 weight percent (based on the total weight of the crystalline propylene polymer composition) of a comonomer;
wherein the crystalline propylene polymer composition is prepared using a single metallocene catalyst system comprising two different metallocene catalyst components; and
wherein the crystalline propylene polymer composition has a molecular weight distribution from 2.1 to 10.
In another embodiment, the invention provides for a film comprising a crystalline propylene polymer composition comprising:
a) from 10 to 90 weight percent of a crystalline, isotactic propylene homopolymer composition comprising a first propylene homopolymer and a second propylene homopolymer, the crystalline, isotactic propylene homopolymer composition having a molecular weight distribution of less than 3; and
b) from 90 to 10 weight percent of a crystalline propylene copolymer composition comprising a first propylene copolymer and a second propylene copolymer, the crystalline propylene copolymer composition having a molecular weight distribution of less than 3, the first propylene copolymer and the second propylene copolymer comprising from 0.05 to 15 weight percent (based on the total weight of the crystalline propylene polymer composition) of a comonomer;
wherein the crystalline propylene polymer composition has a molecular weight distribution in the range of from 2.1 to 10.